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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??
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electrodacus:

--- Quote from: Naej on July 08, 2022, 09:42:44 am ---It appears you don't understand the difference between force and power. Check these out in high school physics books.
For example, the concrete at the bottom of a wind turbine produces 0 W (as most concrete) and can "cancel" the 3MW produced.

Lol and what if the "coefficient of drag" is 0.1 ?

--- End quote ---

This exactly the problem but in reverse.

The reason a wind turbine attached to earth will not seem to move is because the power is applied to entire earth and yes earth will absorb that kinetic energy and spin a bit faster or slower but it all cancels out more or less as wind around the globe will be from different directions.
Plus earth is so massive and his density is so much higher than the very thin atmosphere that it makes no measurable impact (plus the random direction I mentioned).

To put this on another way. In a day with no wind how much power will a wind turbine generate if installed on a vehicle driving at say 10m/s and how much power will vehicle need to compensate for the drag produce by the turbine?

The 0.4 coefficient of drag was selected to match what a 40% efficient wind turbine look like. If wind turbine was just 10% efficient then yes you can consider coefficient of drag 0.1 and if you have a theoretical 100% efficient wind turbine (meaning no air on the other side of the swept area basically a sail) then coefficient of drag will be 1.

So the vehicle can have 0.1 (hard to do) coefficient of drag excluding the wind turbine. Then you install a wind turbine and if that is 40% efficient then the mechanical power it will apply to vehicle due to drag will be at least a theoretical 0.4 drag coefficient else you will claim to violate energy conservation.

So in order for a vehicle to be able to drive direct upwind (no matter how it is designed) it will require an energy storage device.
The simple way to think about this is vehicle applies brakes (basically anchors the vehicle to ground) stored the wind turbine generate energy then uses that to drive against wind direction until stored energy is used up then stops again or at least slows down (uses kinetic stored energy in vehicle mass to coast) charges again and can accelerate again for some time.
In reality there is no large energy storage device in a direct upwind version (as you have with direct down wind) so this charge discharge cycles happen very fast multiple times per second (so fast that you may not even notice with eyes and can only see on a high speed camera).
The other version of direct down wind uses much larger capacity pressure differential energy storage so there a charge discharge cycle take many minutes.     
PlainName:

--- Quote ---So the vehicle can have 0.1 (hard to do) coefficient of drag excluding the wind turbine.
--- End quote ---

It could have a 1.0 coefficient and not have a problem since there is no drag at wind speed, and negative drag below that.
electrodacus:

--- Quote from: dunkemhigh on July 08, 2022, 04:57:55 pm ---
--- Quote ---So the vehicle can have 0.1 (hard to do) coefficient of drag excluding the wind turbine.
--- End quote ---

It could have a 1.0 coefficient and not have a problem since there is no drag at wind speed, and negative drag below that.

--- End quote ---

The discussion was about direct upwind version not direct downwind.
With direct downwind there is no drag at wind speed but there is also no wind power available.
Naej:

--- Quote from: electrodacus on July 08, 2022, 04:25:52 pm ---
--- Quote from: Naej on July 08, 2022, 09:42:44 am ---It appears you don't understand the difference between force and power. Check these out in high school physics books.
For example, the concrete at the bottom of a wind turbine produces 0 W (as most concrete) and can "cancel" the 3MW produced.

Lol and what if the "coefficient of drag" is 0.1 ?

--- End quote ---

This exactly the problem but in reverse.

The reason a wind turbine attached to earth will not seem to move is because the power is applied to entire earth and yes earth will absorb that kinetic energy and spin a bit faster or slower but it all cancels out more or less as wind around the globe will be from different directions.
Plus earth is so massive and his density is so much higher than the very thin atmosphere that it makes no measurable impact (plus the random direction I mentioned).

To put this on another way. In a day with no wind how much power will a wind turbine generate if installed on a vehicle driving at say 10m/s and how much power will vehicle need to compensate for the drag produce by the turbine?

The 0.4 coefficient of drag was selected to match what a 40% efficient wind turbine look like. If wind turbine was just 10% efficient then yes you can consider coefficient of drag 0.1 and if you have a theoretical 100% efficient wind turbine (meaning no air on the other side of the swept area basically a sail) then coefficient of drag will be 1.

So the vehicle can have 0.1 (hard to do) coefficient of drag excluding the wind turbine. Then you install a wind turbine and if that is 40% efficient then the mechanical power it will apply to vehicle due to drag will be at least a theoretical 0.4 drag coefficient else you will claim to violate energy conservation.

So in order for a vehicle to be able to drive direct upwind (no matter how it is designed) it will require an energy storage device.
The simple way to think about this is vehicle applies brakes (basically anchors the vehicle to ground) stored the wind turbine generate energy then uses that to drive against wind direction until stored energy is used up then stops again or at least slows down (uses kinetic stored energy in vehicle mass to coast) charges again and can accelerate again for some time.
In reality there is no large energy storage device in a direct upwind version (as you have with direct down wind) so this charge discharge cycles happen very fast multiple times per second (so fast that you may not even notice with eyes and can only see on a high speed camera).
The other version of direct down wind uses much larger capacity pressure differential energy storage so there a charge discharge cycle take many minutes.     

--- End quote ---
No you don't compute the drag coefficient this way.  ;D
Or are you claiming that the drag coefficient of a wind turbine is 0 ?

In general you seem to believe that whatever you want to be true about energy/forces must be true. It does not work this way. You must learn mechanics first.
electrodacus:

--- Quote from: Naej on July 08, 2022, 09:13:24 pm ---No you don't compute the drag coefficient this way.  ;D
Or are you claiming that the drag coefficient of a wind turbine is 0 ?

In general you seem to believe that whatever you want to be true about energy/forces must be true. It does not work this way. You must learn mechanics first.

--- End quote ---

Not sure what have you read or understood from my comments. So I better provide you the numbers are you seems to be the one having problems with classical mechanics and especially the energy conservation.

If all you have is a wind turbine on wheels say vehicle has negligible frontal area except for the wind turbine that faces directly the wind.
I do not care how the wind turbine is designed or what the wind turbine efficiency is as long as turbine outputs 100W then there will be at a absolute minimum 100W pushing against the vehicle trying to accelerate the vehicle in same direction the air particle move.
So whatever you do with those 100W from the wind turbine you can not advance at any speed against wind direction. The best you can do is stay in place.

The only way to drive upwind with a wind powered vehicle is to use an energy storage device.

You do not need to look at forces at all (you can but is not useful for this particular problem). All you need to know is power in (wind pushing against the vehicle and turbine is part of the vehicle) and power out (power applied at the wheels) which can never be higher than power in unless you add an external energy source or energy from an onboard energy storage device that was charged from available wind energy earlier.

But for direct upwind equivalent you do not even need to bother with air all you need is wheels.  And if you care about forces here it is


Let me know if you think this vehicle can move from left to right using energy from that treadmill that moves in the opposite direction right to left.
If you think that is possible without energy storage please write done the equation. 
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